Engines are classified into the type in which cylinders are serially connected, the type in which cylinders are connected so as to face each other, the V type, and the like in accordance with the arrangement of the cylinders. The V-type engine has a first cylinder bank on one side and a second cylinder bank on the other side. As a V-type engine, there is also a lateral mounting type in which the first and second cylinder banks are installed so as to be located on the front and rear sides with respect to the progressing direction of the vehicle.
There is an oil passage structure of a cylinder head disclosed in the Official Gazette of Japanese Utility Model Registration Application Laid-Open No. 54-127945. According to a valve portion lubricating apparatus of an engine disclosed in the above Official Gazette, an oil pan is provided in a cam portion of a single overhead cam mechanism of the front inclined type engine, a predetermined depth is set in a rear side wall of the oil pan, and a slit is formed so as not to lower the height of the oil surface in the oil pan.
In the conventional oil passage structure of the cylinder head, as shown in FIGS. 8-11, a cam chamber 144 is formed in the upper portion of a cylinder head 108. A plurality of bolt hole portions 140 for cylinder head bolts (not shown) are formed on the exhaust (EX) side of the cam chamber 144. A side wall 146 of the cam chamber 144 is formed so as to isolate the chamber 144 from the cylinder head bolts. An oil passage 142 appears in the inner surface and in the lower portion of the side wall 146 when it is used. Since the side wall 146 of the cam chamber 144 is away from the cylinder head bolts, namely, it is projected toward the intake side, a weir (i.e., barrier) 160 is formed in the lower portion of the oil passage 142. Similarly, the weir 160 is also formed adjacent the bolt hole portions 140. A concave portion 162 is formed in the lower portion of the oil passage 142 by the weir 160.
Thus, there is an inconvenience because the oil can remain in the concave portions such that the oil flow deteriorates and defective oil lubrication is caused. There are also inconveniences in that dust, sludge and the like which are conveyed by the oil precipitate and are deposited in the concave portions and become factors to deteriorate the oil. Therefore, the useful life of the oil becomes short and the frequency of oil changes increases, which is economically disadvantageous. Further, since a pulsation (i.e., turbulence) occurs in the oil as it flows by the concave portions, air can be mixed into the oil easily, and various disadvantages are caused by the air mixture.
In an attempt to eliminate the above inconveniences, in an oil passage provided on the exhaust side of the cylinder head to perform lubrication in a cam chamber which is formed in the upper portion of the cylinder head, the invention is characterized in that bolt hole portions for cylinder head bolts to attach the cylinder head to a cylinder block are provided, the height of a bearing surface of each bolt hole portion is set to a large value, and the oil passage extending in the longitudinal direction of the cam chamber of the engine is provided in the cylinder head below the bearing surface.
According to the invention as mentioned above, the oil smoothly flows in the oil passage in the cam chamber of the cylinder head. Inadequate lubrication can be prevented. Amounts of precipitation and deposition of dust, sludge and the like which are conveyed by the oil are reduced. The amount of air mixed into the oil is reduced.